The present invention relates to a fitting for connecting an antenna. More particularly, it relates to a fitting for connecting an antenna in a hazardous area environment to an electrical enclosure such as an explosion-proof enclosure, a safe area enclosure, or to an electrical conduit.
The length of an antenna depends on the frequency of the transmitted signal. Therefore, for different frequencies of transmission, and for different radio receivers and transmitters, it may be necessary to have different length antennas. Standards for installation of electrical equipment in hazardous area environments require that the installation comply with two types of protection:
an intrinsically safe barrier which will suppress an electrical surge which may potentially travel through the device, and
an explosion-proof device enclosure to withstand the maximum anticipated force of an explosion.
Prior art methods for complying with these standards as they relate to antennas include the use of a capacitive block circuit inside the explosion-proof or safe area enclosure to provide the intrinsically safe barrier, and/or an antenna which has been completely encased in a hazardous area sealing compound. This encased antenna is intended to be mounted directly to the electrical enclosure. If the electrical enclosure is not immediately adjacent to the antenna, and is instead separated from the enclosure by a conduit, then sealing fittings are required both where the antenna mounts to the conduit and where the conduit connects to the enclosure. The installation of sealing fittings is expensive, labor intensive, and time consuming (the sealing compound must be allowed to cure after it is injected into the sealing fitting).
This prior art method is highly inflexible. If the encased antenna was incorrectly specified or supplied, or if the receiver or transmitter must be replaced with one of different frequency, or if the encased antenna is accidentally damaged, there is no simple manner to replace the antenna. The entire encased antenna (and any sealing fittings installed adjacent to the antenna) must be replaced. This is expensive and time consuming.